Wednesday Colloquium


"Extreme quasars at high redshift"

Mary Loli Martinez Aldama (Center for Theoretical Physics, PAN, Warsaw)

The study of the AGN accreting close to the Eddington limit (L/LEdd~1) has taken an important role, due to their potential use as standard candles for cosmological applications. With the purpose to understand the physics of extreme quasar, we perform a spectroscopic analysis of a sample of highly accreting quasars at high redshift (z~2–3). Our sample were observed with the OSIRIS spectrograph on the GTC 10.4 m telescope located at the Observatorio del Roque de los Muchachos in La Palma. The highly accreting quasars were identified using the 4D Eigenvector 1 formalism, which is able to organize type 1 quasars over a broad range of redshift and luminosity. The kinematic and physical properties of the broad line region have been derived by fitting the profiles of strong UV emission lines such as AlIII λ1860, SiIII]λ1892 and CIII]λ1909. We find that AlIIIλ1860 can be associated with a low-ionization virialized sub-system. xA sources show strong blueshifts in the high-ionization lines like in CIVλ1549, indicating a relation between the high Eddington ratios and the productions of outflows. The extreme radiative properties of highly accreting quasar make them prime candidates for maximum feedback effects on the host galaxy. The characterization of extreme quasar allow to assemble large samples of extreme quasars from the latest data releases of the SDSS, especially useful for deriving independent estimates of ΩM in the redshift range 1


"Mapping the close environments to the event horizon with NICER"

Phil Uttley (Astronomical Institute Anton Pannekoek Universiteit van Amsterdam)

X-ray spectral-timing is an approach to studying the X-ray variability of accreting compact objects, which combines photon energies and arrival-times to determine the causal relationship between the emission components. With this approach, we are starting to ‘map’ the innermost regions of accreting black hole systems. In this talk I will review this growing field in X-ray astronomy and show how it is being further revolutionised by remarkable results from the the Neutron star Interior Composition Explorer (NICER), which was installed on the International Space Station last year. NICER has an unprecedented capability to study the brightest X-ray sources in the sky - X-ray binaries - with no instrumental distortion or telemetry losses, even for count rates above 1e4 counts per second.


"Tidally induced bars in Illustris galaxies"

Nicolas Peschken (CAMK, Warsaw)

Galactic bars are a central elongated stellar structure found in the center of many disc galaxies, such as the Milky Way. Those bars are central for the study of disc galaxies, as they impact the whole disc structure and morphology, for both the gas and stars. Their formation mechanisms are diverse, as they can form in secular evolution, or be triggered by external perturbers. I will present my work about the study of galactic bars in Illustris, a large hydrodynamical cosmological simulation with hundred thousands of galaxies. After presenting the general properties of bars and the bar frequency in Illustris disc galaxies, I will focus on bars tidally induced, i.e. when the bar forms from an interaction with another galaxy.


"SALT: Status and new developments"

Petri Vaisanen (SAAO)

I will summarise the current status of SALT, the 10m optical telescope in South Africa, including its instruments and some recent science results. I will in particular highlight the new science strategy adopted recently to focus the future work and collaborations. I will talk about the instrumentation development plans for the next years supporting those science goals, and how these could benefit the Polish astronomical community.

"GW 170817 and its Electromagnetic Counterparts - what was confirmed and what have we learned?"

Tsvi Piran (The Hebrew University of Jerusalem)

The observed GRB (170817A) that followed GW170817 confirmed the longstanding prediction of association of short GRBs with neutron star mergers. The unique large scale observational campaign that followed confirmed further predictions, and in particular that mergers are the dominant sites of r-process nucleosynthesis. They also provided numerous surprising observations, teaching us a lot about these events. . I discuss past predictions, current observations and their implications and future prospects of joint detection of GRBs and GW signals. Among the latter, most exciting is the possibility that the gravitational waves observations will teach us about the inner working of GRBs central engine and the acceleration process of relativistic jets.

Attention: Tsvi Piran's Colloquium will start at 2:15 pm


"Multi-wavelength Variability and QPOs in Blazars"

Alok Chandra Gupta (Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital, India)